This is how to cure ring worms on horse's in 7 steps. 1. Call your vet. asap. 2. Clip hair away from affected area. 3. Spot-bathe the lesions. 4. Apply an antifungal dressing. 5. Keep lesions clean, dry, and exposed to air and sun. 6. Disinfect your premises and yourself. 7. Evaluate your horse's progress.